1. Field of the Invention
The present invention relates to a bearing lubricant composition.
2. Description of the Related Art
The miniaturization and low power consumption of the electronic apparatuses, such as home electrical appliances, electronic and information products, industrial machines, and mobile terminals, progress every year. The usable temperature ranges of these electronic apparatuses also expand every year. With these trends, spindle motors in which fluid bearings (fluid dynamic bearings), etc., are mounted, have been used in disk drive devices to be used in these electronic apparatuses.
The miniaturization and low power consumption of these electronic apparatuses, and the expansion of the usable temperature ranges thereof are achieved mostly by improvements in the performances of motors. One of the means for achieving an improvement in the performance of a motor or a device in which the motor is mounted is to enhance the performance of a bearing, such as a fluid bearing, which is mounted in the motor. Accordingly, in order to achieve an improvement in the performance of a bearing, various bearing lubricant compositions have been presented (see, for example, Patent Documents 1 and 2).
[Patent Document 1] International Patent Application Pamphlet No. 2004/018595
[Patent Document 2] Japanese Patent Application Publication No. 2008-7741
In recent years, there is an increasing demand for expanding the usable temperature ranges of these electronic apparatuses. In particular, there is a need for expanding the applications of these electronic apparatuses to mobile apparatuses, and hence motors and devices in which the motors are mounted are required to withstand the use under severer temperature environments. That is, there is a strong demand that the usable temperature ranges of motors and devices in which the motors are mounted should be expanded and they should be stably driven when temperature changes. Accordingly, bearing lubricant compositions are also required to have expanded usable temperature ranges and have small changes in viscosity with temperature.